1) Field of the Invention
The present invention relates to transmitters and a method of transmission that are used in a network where data packets are transferred between a source transmitter and a destination transmitter via a relay transmitter, and relates more particularly to transmitters and a transmission method that are suitably employed in a vast and complex network where data transmission between certain points is performed via a redundant path structure (consisting of a plurality of paths) to ensure reliability.
2) Description of the Related Art
In networks, in which transmission path ports in transmitters are connected through transmission paths such as optical fiber paths, data communications is performed between transmitters.
In a first method of transmission, it is judged whether a data packet received by one transmission path port in a transmitter is relayed to another transmission path port which relays the received data packet to its destination, and based on the result of judgement, the received data packet is relayed from the receiving port to the relay port. In a second method of transmission, a transmission path port to relay a data packet is determined by referring to a routing table, based on a destination address contained in the header of a data packet.
A conventional transmitter adopting the above-described first transmission method is shown in FIG. 12 by way of example. The conventional transmitter is typically configured to include receiving port sections 111, 121, 131, 141, transmitting port sections 112, 122, 132, 142, and a relay section 150.
The receiving port sections 111, 121, 131, and 141 consist of O/E (Optical/Electrical) converters 113, 123, 133, 143, reception controllers 114, 124, 134, 144, and first-in first-out (FIFO) memories 115, 125, 135, 145, respectively. The transmitting port sections 112, 122, 132, and 142 consist of transmission controllers 116, 126, 136, 146, FIFO memories 117, 127, 137, 147, and E/O converters 118, 128, 138, 148, respectively.
The relay section 150 consists of relay units 151 to 154, which relay packets received via the receiving port sections 111, 121, 131, and 141. The relay units 151 to 154 store the connection status of the transmitting port sections 112, 122, 132, and 142 to which a received packet is transmitted from the receiving port sections 111, 121, 131, and 141. This makes it possible to relay a packet received via the receiving ports 111, 121, 131, or 141 to a relay transmitter from which the received packet reaches its destination (destination transmitter).
For example, in the case where transmitters 1-1 to 1-n (where n is an integer≧3), 2-1 to 2-4, 3-1, and 3-2 such as the one shown in FIG. 12 are arranged as shown in FIG. 13 and construct a network 4, packets are transmitted within the network 4 by the above-described first transmission method. In the relay units 151 to 154 of the relay section 150 in each of the transmitters 1-1 to 1-n, 2-1 to 2-4, 3-1, and 3-2, relay methods in the transmitting and receiving port sections 111, 121, 131, 141, 112, 122, 132, and 142 are set.
The network 4 consists of three network portions, depending on the form of connection of transmitters. The first network portion 1 consists of transmitters 1-1 to 1-n connected in tandem, the second network portion 2 consists of transmitters 2-1 to 2-4 connected in ring form, and the third network portion 3 consists of transmitters 3-1 and 3-2 connected in tandem. The transmitter 1-n and the transmitter 2-1 are connected to each other, so the first network portion 1 and the second network portion 2 are connected to each other. The transmitter 2-4 and the transmitter 3-1 are connected to each other, so the second network portion 2 and the third network portion 3 are connected to each other.
The transmitter 2-1 is constructed so packets can be relayed according to settings shown in FIG. 14 by the relay units 151 to 154 of the relay section 150. Note in the figure that the transmission path ports 110, 120, 130, and 140 of the transmitter 2-1 are provided with transmitting and receiving port sections 112 and 111, transmitting and receiving port sections 122 and 121, transmitting and receiving port sections 132 and 131, and transmitting and receiving port sections 142 and 141 (see FIG. 12).
More specifically, the first transmission path port 110 is provided with the receiving port section 111 for receiving packets from the transmitters 1-n, and the transmitting port section 112 for transmitting packets to those transmitters 1-n. Similarly, the second transmission path port 120 is provided with the transmitting port section 122 and receiving port section 121 for transmitting and receiving packets to and from the transmitter 2-2. The third transmission path port 130 is provided with the transmitting port section 132 and receiving port section 131 for transmitting and receiving packets to and from the transmitter 2-4.
In the network 4 shown in FIG. 13, in order to perform communications from the transmitter 2-4 to the transmitter 2-2, in the relay transmitter 2-1 data packet received from the transmission path port 130 is relayed to the transmission path port 120. To perform communications from the transmitter 2-4 to the transmitters 1-1 to 1-n, the data packet from the transmission path port 130 is also relayed to the transmission path port 110. In other words, the data packet received by the receiving port section 131 of the transmission path port 130 is copied in the relay unit 153 of the transmitter 2-1 and relayed to the transmitters 1-1 to 1-n and to the transmitter 2-2.
Likewise, to perform communications from the transmitter 2-2 to the transmitter 2-4, a data packet received from the transmission path port 120 is relayed to the transmission path port 130. To perform communications from the transmitter 2-2 to the transmitters 1-1 to 1-n, the data packet from the transmission path port 120 is also relayed to the transmission path port 110. In other words, the data packet received by the receiving port section 121 of the transmission path port 120 is copied in the relay unit 152 and relayed to the transmitters 1-1 to 1-n and transmitter 2-4.
In addition, to perform communications from the transmitters 1-1 to 1-n to the transmitter 2-2, a data packet received from the transmission path port 110 is relayed to the transmission path port 120. To perform communications from the transmitters 1-1 to 1-n to the transmitter 2-4, the data packet from the transmission path port 110 is also relayed to the transmission path port 130. In other words, the data packet received by the receiving port section 111 of the transmission path port 110 is copied in the relay unit 151 and relayed to the transmitter 2-4.
Another conventional transmitter adopting the above-described second transmission method is shown in FIG. 15. The transmitter, as with the transmitter shown in FIG. 12, includes receiving port sections 111, 121, 131, 141, transmitting port sections 112, 122, 132, 142, and a relay section 160.
Unlike the case of FIG. 12, the relay section 160 consists of a routing processing section 170 and a table register 180. The routing processing section 170 is equipped with a receiving part 171, a destination address extracting part 172, a judging part 173, and four transmitting parts 174 to 177. The table register 180 dynamically or statically stores a transmitting port number for relaying data for each destination address.
More specifically, in the routing processing section 170 of the transmitter adopting the second transmission method shown in FIG. 15, the destination address extracting part 172 extracts a destination transmitter address (destination address, DA) from the header of a data packet received by each of the receiving port sections 111, 121, 131, and 141. The judging part 173 extracts the number of the transmitting port section 112, 122, 132, or 142 connected with a destination transmitter, by referring to the statically or dynamically set table register 180. The judging part 173 further commands the transmitting parts 174, 175, 176, and 177 connected with the extracted transmitting port sections 112, 122, 132, and 142 to transfer data packets received by the receiving part 171.
For instance, in a network 4A with transmitters 5-1, 5-2, 6, 7, 8-1, 8-2, and 9 connected as shown in FIG. 16, when packets are transmitted by the above-described second transmission method, each of the transmitters 5-1, 5-2, 6, 7, 8-1, 8-2, and 9 is constructed as shown in FIG. 15.
Note that the network 4A has a redundant transmission path structure between the transmitters 7 and 9, which consists two routes. In the first route, packets are relayed to the transmitter 8-1 connected to the transmission path port 140. In the second route, packets are relayed to the transmitter 8-2 connected to the transmission path port 130.
In the relay transmitter 7, a data packet is relayed according to settings shown in FIG. 17 by the routing processing section 170 of the relay section 160. That is, a destination address (DA) in the header of a data packet (DP), received by the receiving port section 111 of the transmission path port 110 (see FIG. 15), is extracted by the destination address extracting part 172. When the extracted destination address is the address of the transmitter 9, that data packet DP is transferred to the transmission path port 140. In this way, the data packet DP received by the transmitter 7 is transferred to the transmitter 9 via the transmitter 8-1.
Note that in order to construct a virtual local area network (VLAN), conventional network frame relay units store information about the corresponding relationship between the address of a terminal in the destination of a network frame and a port connected to that terminal, and also store information about the corresponding relationship between the address of a terminal in the source of a network frame and a port connected to a terminal in the destination of a network frame transmitted from the address of that source terminal (see Japanese Laid-Open Patent Publication No. HEI 9-186715).
In addition, in conventional packet switches, if a packet is received, an IP flow table is searched for the IP source address and IP destination address of that packet in order to reduce microprocessor's routing load and security load. If the IP flow table has a corresponding IP flow, the packet is transferred to an appropriate output port according to the routing process shown in the IP flow without being routed by a microprocessor (see Japanese Laid-Open Patent Publication No. 2000-295274).
However, the network 4 shown in FIG. 13 has the following problems when transmitting data packets by the aforementioned first transmission method, using transmitters such as that shown in FIG. 12.
For instance, if a data packet is transmitted from the transmitter 3-2 to the transmitter 1-1, the data packet is copied in the relay section 150 of the transmitter 2-1 and is relayed to the transmission path port 110 connected with the transmitters 1-1 to 1-n and to the transmission path port 120 connected with the transmitter 2-2. Because of this, the data packet relayed to the transmitter 2-2 returns to the transmitter 2-1 through the transmitters 2-3 and 2-4. Since the network portion 2 in the form of a ring has a closed transmission path, data packets can circulate through the ring path.
In the above-described case, the transmitter 2-1 relays a data packet toward the transmitter 2-2 as well as to the transmitter 1-1, so the data packet is also added onto the ring network portion 2. To avoid this, the number of hops (the number of relays from the transmitter 2-4 to the transmitter 1-1) is typically set to the header of a data packet, and a subtraction is made each time the data packet is relayed. After a predetermined number of relays, the data packet is discarded.
However, if a distance to the transmitter 1 (the number of hops) is long like the network 4 shown in FIG. 13 (particularly, if the value of n in reference numeral “1-n” is 4 or more, and 4 or more transmitters are connected in tandem), the number of hops at the transmitter 2-1 will reach a predetermined number.
If, in the network 4, a data packet is transmitted from the transmitters 1-1 to 1-n to the transmitters 2-2 to 2-4, data congestion will easily occur in the transmission path port 120 of the transmitter 2-1 because of the presence of data packets being circulated through the ring network portion 2, and consequently, an increase in traffic and the loss of transmitted packets will easily occur.
In the case where a network like FIG. 13 is constructed with transmitters having the same structure as that shown in FIG. 15, a data packet can be relayed only to a specified transmitter and therefore it is possible to solve the above-described problems, but since transmitting special data packets (such as multi-address transmission) is the equivalent of transmitting multi-destination packets, the same data congestion as the case of the above-described network 4 sometimes occurs. In this case, the problem of an increase in traffic and the loss of transmitted packets will easily arise and result in a reduction in the quality of transmission paths.
In addition, the network 4A shown in FIG. 16 has the following problems when transmitting data packets by the aforementioned second transmission method.
As shown in FIG. 16, both a data packet to be transmitted from the transmitter 5-1 to the transmitter 9 and a data packet to be transmitted from the transmitter 5-2 to the transmitter 9 have the same destination address, and the relay transmitter 7 relays these data packets through the same transmission path port without discriminating between the two.
In that case, the two data packets are transferred to the transmitter 9 through the same route (connected to the transmission path port 130), even when the path between the transmitters 7 and 9 has a redundant transmission path structure. Because of this, the network load on the route onto which data packets were transmitted is increased, and consequently, an increase in traffic and the loss of transmitted packets tend to take place.
On the other hand, even if the transmitter 7 relayed data packets to both ports in the manner shown in FIG. 12, the same data packet would be copied and transmitted and the traffic between the transmitters 7 and 9 would double.
The technique described in the aforementioned Japanese Laid-Open Patent Publication No. HEI 9-186715 is a technique to construct a virtual local area network (VLAN). Therefore, even if this technique is used in the transmitters of the networks 4 and 4A shown in FIGS. 13 and 16, an increase in traffic and the loss of transmitted packets can not be prevented.
In addition, the technique described in the aforementioned Japanese Laid-Open Patent Publication No. 2000-295274 is a technique for reducing microprocessor's routing load and security load. Therefore, even if this technique is employed in the transmitters of the networks 4 and 4A shown in FIGS. 13 and 16, an increase in traffic and the loss of transmitted packets can not be prevented.